Phelps wins 100m fly qualification in comeback

Michael Phelps warms up in the practice pool during day one of the Arena Grand Prix at the Skyline Aquatic Center on April 24, 2014 in Mesa, Arizona.

US swimmer and Olympic gold medalist Michael Phelps has qualified fastest for the 100-meter butterfly final in his first competition since retiring after the 2012 London Olympics.

He won the race at the Arena Grand Prix in 52.84 seconds and advanced to the evening final in Mesa, Arizona.

Phelps is the world and US record holder in the 100 fly. He became the first man to win the same event at three consecutive Olympics when he captured gold in London.

Phelps and his coach Bob Bowman were both reluctant to talk about their long term goals when they appeared at a packed news conference on the eve of his comeback but they did not rule out the possibility of competing at the 2016 Rio Olympics.

Unshaven and still seven pounds (three kilograms) over his ideal racing weight, Phelps had planned to swim in three events at his comeback meet but ditched the 100m freestyle to focus on the 100m butterfly and Friday's 50m freestyle.

Tickets for the event sold out within hours after Phelps confirmed he was making his comeback and were selling for more than five times their face value on the secondary market.

More than 100 media - a 500 per cent increase on last year's meet - descended on the Skyline Aquatic Center to see him take his first plunge back into the water.